Fermentation weight

A fermentation weight is a heavy, food safe object placed on top of shredded or whole vegetables to keep them pressed down under the brine. Since lactic acid bacteria need an oxygen-poor environment to thrive, and mold needs air to grow, keeping every piece of vegetable submerged is one of the most important habits in vegetable fermentation.

Weights come in several forms, including glass discs sized for wide-mouth jars, ceramic pucks made for fermentation crocks, and flexible silicone options that mold to the shape of the container. Some fermenters improvise with a smaller jar filled with water, a boiled stone, or a cabbage leaf tucked over the shredded vegetables, though purpose-made weights tend to fit more snugly and are easier to clean.

The most common problem weights solve is floating vegetable scraps, which dry out above the brine line and can develop mold within a day or two. A weight that is too light or an odd-shaped jar can let pieces slip around the edges, so it helps to check on a new ferment daily for the first few days and press everything back under if needed.